A multidomain galectin involved in innate immune response of pearl oyster Pinctada fucata

Galectins could specifically bind to β-galactoside residues and play crucial roles in innate immune responses of vertebrates and invertebrates. In this study, the cDNA of a galectin with multiple carbohydrate-recognition domains (CRDs) was cloned from pearl oyster Pinctada fucata (designated as PoGal). PoGal cDNA was 2138bp long and consisted of a 5'-untranslated region (UTR) of 120bp, a 3'-UTR of 350bp with two cytokine RNA instability motifs (ATTTA), and an open reading frame (ORF) of 1668bp encoding a polypeptide of 555 amino acids with an estimated molecular mass of 63.4kDa and a theoretical isoelectric point of 4.8. PoGal contained four CRDs, each CRD of PoGal all had the conserved carbohydrate-binding motifs H-NPR and WG-ER. PoGal shared 43.7% and 62.9% identity to those of bay scallop and eastern oyster, respectively, which were only two galectins with four CRDs. The phylogenetic analysis revealed that all galectins with four CRDs formed a single clade. PoGal mRNA was constitutively expressed in all detected tissues, and the expression level of PoGal mRNA was significantly up-regulated in digestive gland, mantle, haemocyte, gonad and intestine after Vibrio alginolyticus stimulation. The expression profile analysis showed that the expression level of PoGal mRNA was significantly up-regulated at 4, 8 and 12h after V. alginolyticus stimulation. These results suggested that PoGal was a constitutive and inducible acute-phase protein that perhaps involved in innate immune response of pearl oyster.